cbcvebase.
CVE-2015-7871
published 2017-08-07

CVE-2015-7871: Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.

PriorityP184critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EXPLOIT
EPSS
81.76%
99.6th percentile
Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.

Affected

11 ranges
VendorProductVersion rangeFixed in
ciscoproducts_october_2015
debiandebian_linux
debiandebian_linux
debiandebian_linux
debianntp< ntp 1:4.2.8p4+dfsg-1 (bullseye)ntp 1:4.2.8p4+dfsg-1 (bullseye)
ntpntp
ntpntp
ntpntp>= 0 < 1:4.2.8p4+dfsg-11:4.2.8p4+dfsg-1
ntpntp>= 0 < 1:4.2.6.p5+dfsg-3ubuntu2.14.04.51:4.2.6.p5+dfsg-3ubuntu2.14.04.5
ntpntp>= 4.2.6 < 4.2.84.2.8
ntpntp>= 4.3.0 < 4.3.774.3.77

Detection & IOCsextracted from sources · hover to see the quote

port123/UDP
  • Detect unauthenticated symmetric active Crypto-NAK packets sent to ntpd on UDP/123; an off-path attacker transmits these to force ntpd to peer with attacker-controlled time sources.
  • Monitor ntpd for unexpected new peer associations being established without prior authenticated exchange, especially ephemeral symmetric peers not in the configured peer list.
  • Alert on ntpd declaring previously legitimate configured peers as 'false tickers', which may indicate an active CVE-2015-7871 exploitation attempt shifting time authority to rogue peers.
  • Look for the PEVNT_AUTH / crypto_NAK event in ntpd logs (report_event with 'crypto_NAK' string) combined with peer flash flag TEST5 (bad auth) being set on an ephemeral association.
  • ·NTP 4.2.6 is NOT vulnerable to exploitation: while an ephemeral association can be temporarily created by the Crypto-NAK, it is immediately torn down via unpeer(), preventing any time manipulation.
  • ·Red Hat Enterprise Linux 5, 6, and 7 ship NTP versions that are not affected by CVE-2015-7871; do not prioritize patching effort on those platforms for this specific CVE.
  • ·The NTP service is deactivated by default on Siemens RUGGEDCOM ROX I and ROX II devices; attack surface only exists when NTP service is explicitly enabled.

CVSS provenance

nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvdv2.07.5HIGHAV:N/AC:L/Au:N/C:P/I:P/A:P
osv9.8CRITICAL
vendor_debian9.8CRITICAL
vendor_redhat9.8CRITICAL
vendor_cisco7.5HIGH
vendor_ubuntu5.3MEDIUM
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